The periods with continuous freezing air temperatures reported during the spring of 2020 (13 incidents) affected a wide range of local and introduced sweet cherry cultivars in the region of Plovdiv. They vary from -0.6°C on March 02 to -4.9°C on March 16-17. The duration of influence of the lowest temperatures is 6 and 12 hours between March 16 and 17. The inspection of fruit buds and flowers was conducted twice (on March 26 and April 08) at different phenological stages after continuous waves of cold weather conditions alternated with high temperatures. During the phenological phase ‘bud burst’ (tight cluster or BBCH 55) some of the flowers in the buds did not develop further making the damage hardly detectable. The most damaged are hybrid El.28-21 (95.00%), ‘Van’ (91.89%) and ‘Bing’ (89.41%) and from the next group ‘Lapins’ (85.98%) and ‘Rosita’ (83.33%). A larger intermediate group form ‘Kossara’ (81.67%), ‘Rozalina’ (76.00%), ‘Sunburst’ (75.00%), ‘Bigarreau Burlat’ (69.11%) and ‘Kuklenska belitza’ (66.67%). Candidate-cultivar El.17-90 ‘Asparuh’ has the lowest frost damage values of 55.00% and El.17-37 ‘Tzvetina’ with damage of 50.60%.

In the conditions of global climate change and invasion of new diseases and pests, the utilisation of the local gene pool is a vital step towards sustainable agriculture. Local cultivars and forms are generally considered as better adapted to the conditions of the originating region than widely spread commercial cultivars bred elsewhere. In order to collect, study, and preserve old and local fruit and vine cultivars and forms, a series of expeditions have been conducted throughout Bulgaria under the frame of project KP-06-N46/3 funded by the National Science Fund of the Bulgarian Ministry of Education and Science. During these scientific expeditions, several local cherry forms were discovered without visual symptoms of brown rot Monilinia laxa (Aderh. and Ruhl.) Honey or cherry leaf spot Blumeriella jaapii (Rehm) Arx. To confirm the degree of resistance/low susceptibility of the specimens, laboratory tests with artificial inoculations of fruits and leaves were conducted. In the current study, two specimens found in Damyanovo region (a village in the municipality of Sevlievo, Gabrovo Province, in northern central Bulgaria) were included. They were compared to two old local cherry cultivars, ‘Volsko sartse’ and ‘Ranna cherna edra’, and two new selections of FGI-Plovdiv, ‘Asparukh’ (El.17-90) and ‘Kossara’, using ‘Bigarreau Burlat’ as reference cultivar for resistance to economically important diseases. The artificial inoculations confirmed the field observation of the cherry specimen with designation SM-58 with 0.00% of infected fruits. Therefore, it is recommended for use in the breeding programme of the Fruit Growing Institute, Plovdiv for the creation of new cultivars.

Fruit growing is a traditional component of Bulgarian agricultural production. According to the latest statistical data, the share of areas planted with cherries is 10.5% of the total orchard area, and with apples, 7.2%, totaling 67,800 ha. This article presents the results of ground and remote (satellite) measurements and observations of cherry and apple orchards, along with the methods for their processing and interpretation, to define the current state and forecast their expected development. This research aims to combine the capabilities of the two approaches by improving and expanding observation and forecasting activities. Ground-based measurements and observations consider the dates of a permanent transition in air temperature above 5 °C and several cardinal phenological stages, based on the idea that a certain temperature sum (CU, GDH, GDD) must accumulate to move from one phenological stage to another. The obtained data were statistically analyzed, and by means of classification with the Random Forest algorithm, the dates for the occurrence of the stages of bud break, flowering, and fruit ripening in the development of cherry and apple orchards were predicted with an accuracy of −6 to +2 days. Satellite studies include creating a database of Sentinel-2 digital images across different spectral bands for the studied orchards, investigating various post-processing approaches, and deriving indicators of developmental phenostages. Ground data from the 2021–2023 experiment in Kyustendil and Plovdiv were used to determine the phases of fruit bursting, flowering, and ripening through satellite images. An assessment of the two approaches to predicting the development of the accuracy of the models was carried out by comparing their predictions for bud swelling and bursting (BBCH 57), flowering (BBCH 65), and fruit ripening (BBCH 87/89) of the observed phenological events in the two selected orchard types, representatives of stone and pome fruit species.

ISHS II International Workshop on Bacterial Diseases of Stone Fruits and Nuts Diversity and host range of Pseudomonas in fruit tree species in Latvia

Research was conducted at the Agricultural Experiment Station—Khan Krum, Northeast Bulgaria during the period of 2014–2017. The aim of the study is to investigate the suitability of selected hybrids No.20-181 and No.20-192, obtained by interspecific crossing ‘Polevka’ (Prunus cerasus L.) × ‘Compact Van’ (Prunus avium L.) as clonal rootstocks for sour cherries. The rootstocks were grafted in a nursery with the cultivars ‘M-15’, ‘Nefris’, ‘Fanal’ and ‘Schattenmorelle’. Prunus mahaleb seedlings were used as the standard for comparison. Characteristics determining growth, the quality of the planting material and the compatibility of the rootstocks with commercial cultivars were tested. The average grafting success rate reported in the spring of the analyzed cultivar–rootstock combinations varied as follows: P. mahaleb (83–90%), hybrid No.20-192 (87–91%) and hybrid No.20-181 (82–85%). The selected hybrid 20-192 (‘Argo 2’) rootstock produces relatively weaker growth than the mahaleb. Hybrid 20-181 (‘Argo 1’) is characterized by the weakest growth. Both tested rootstock hybrids produce planting material with standard trunk diameter and tree height. With the weak growth that rootstock 20-181 induces in the grafted cultivar and the drought tolerance observed in 20-192, it is appropriate to continue the study in an orchard.